薄壁结构后屈曲应力分析

研究薄壁结构的蒙皮因压，剪失稳后的承力特性和后屈曲有限元分析方法，文中给出了翘曲边形的非对角张力场有限元计算模型和相应的张力场单元刚度矩阵，并进行了实验验证，最后通过若干实例说明了方法和程序的可靠性及实用性。     

POST-BUCKLING ANALYSIS WITH FRICTIONAL CONTACTS COMBINING COMPLEMENTARITY RELATIONS AND AN ARC-LENGTH METHOD

A linear complementarity problem formulation combined with an arc-length method is presented for post-buckling analysis of geometrically non-linear structures with frictional contact constraints. The arc-length method with updated normal plane constraint is used to trace the equilibrium paths of the structures after limit points. Under the proportional loading assumption, the unknown load scale parameter used in the arc-length method is expressed in terms of contact forces, and eliminated to formulate as a linear complementarity problem. The unknown contact variables such as contact status and contact forces can be directly solved in this formulation without any ad hoc technique. Complicated non-linear buckling behaviours, such as snap-buckling, can be efficiently solved by the developed method, as shown by several buckling and post-buckling problems with frictional contact constraints.     

双向增强体复合地基桩土应力比计算

针对竖向增强体-水平增强体-桩间土的整体相互作用特点,将水平向加筋垫层视为具有一定刚度的板,竖向桩体及桩间土简化为刚度不同的弹簧系列。以单个竖向桩体影响范围内的复合地基作为典型单元体进行分析,基于Winkler弹性地基圆板理论推导出水平加筋体的挠曲函数表达式,导出双向增强体复合地基桩土应力比计算式。最后对某工程算例进行计算分析,对路堤荷载大小、工后沉降值、面积置换率、桩土刚度比进行了参数研究,并探讨了桩土应力比随其主要影响因素的变化规律,计算与实测结果吻合较好。     

中国现行钢结构规范(规程)与美国ASD规范的主要限值

通过比较现行中、美两国的钢结构设计规范、规程中对受压杆件的长细比、翼缘宽厚比、腹板高厚比的极限值规定,阐述两国规范、规程中的差异和近似之处。     

Applicability of simple intuitive formulation for predicting thermal post-buckling behaviour of columns resting on hardening nonlinear elastic foundation

The paper demonstrates the applicability of a simple intuitive formulation, the development of which started around a decade ago in obtaining the thermal post-buckling behaviour of uniformly heated slender columns that rest on hardening nonlinear Winkler foundation. This foundation, which is firmly bonded to the column, is idealised by a number of closely spaced hardening nonlinear elastic springs. The nonlinear foundation stiffness of the nonlinear elastic foundation is dependent on the square of the deflection of the columns. Analytical expressions for the thermal post-buckling loads, for the buckled mode shapes with wave number one, by applying the concept of smart structures, of the commonly used columns on hardening nonlinear foundation are derived, by using a simple, intuitive formulation. The numerical results presented are validated, by comparing from those obtained for the limiting cases and non-violation of the physical and logical behaviour, in the absence of any similar results available in literature. These results reveal, the relative contributions of the various parameters existing in the hardening nonlinear Winkler foundation, on the thermal post-buckling behaviour of hinged–hinged and clamped–clamped columns.     

节点域斜加劲肋设计计算方法

我国现行钢结构设计规范与规程对梁柱节点域的抗剪能力提出了具体的要求,并指出当节点域抗剪能力不足时可设置斜向加劲肋。但是却没有给出所设置的斜加劲肋的计算办法。采用有限单元法对考虑了斜肋板宽厚比、腹板宽厚比、节点域高宽比、柱翼缘宽厚比等多种影响因素的节点域模型进行了屈曲后强度计算,分析了各种不同情况下的节点域的变形及应力分布,提出了有斜加劲肋的节点域的等效计算模型及计算公式,并推导了门式刚架节点域斜加劲肋的设计计算公式。     

基于m法的高承台嵌岩灌注桩初始后屈曲性状分析

为探讨桥梁工程中广泛使用的高承台嵌岩灌注桩初始后屈曲性状,先将桩身视为部分支承的Winkler地基梁,基于m法建立桩土体系总势能方程;然后采用扰动法,由最小势能原理导得初始后屈曲过程中桩顶临界荷载的一般变化式,并以此讨论3种特殊情况下桩身初始后屈曲平衡路径的稳定性。结果表明,初始后屈曲过程中的桩身平衡分枝点具有对称性,但是否稳定则取决于桩土刚度比、桩顶自由长度等系统参数。通常,桩周土刚度越大,桩身初始后屈曲平衡路径越趋于稳定。但当桩身刚度一定而桩周土越趋于软弱时,桩底嵌岩对桩身初始后屈曲平衡路径的稳定有利,否则将更趋于不稳定。     

薄壳极值型后屈曲分析的一种有效数值方案

本文简略讨论了薄壳非线性屈曲有限元分析中传统增量mN-R迭代法能快速收敛的优点和不能跟踪后屈曲平衡路径的原因,并提出了改进方案.算例表明:改进算法在薄壳极值型后屈曲分析中具有较高的计算精度.     

The Lagrange problem on an optimal column: old and new results

The paper is devoted to the optimization and post-buckling behavior of columns elastically supported at both ends. The unimodal solutions are analyzed, and it is shown that for nonzero support stiffnesses they are not optimal. The bimodal formulation of the problem is set up. By using analytical expressions for bimodal columns obtained earlier, the bimodal optimal solutions are integrated for different values of the support stiffnesses. With the assumption of geometrical nonlinearity, the post-buckling behavior of the bimodal optimal columns is studied. It is shown that the initial post-buckling behavior is governed by four supercritical solutions emanating from the trivial equilibrium state at the critical load. The stability of the new equilibrium states is investigated by using the second variation of the total potential energy. It is shown that only two post-buckling equilibrium states are stable while the other two are unstable, this conclusion being valid for all considered values of the support stiffnesses. An important limit case of a clamped–simply supported column that has caused debate in many publications is analyzed.